1. Field of the Invention
The present invention relates to gate valve systems of the type used on tank trucks, especially those used for carrying hazardous waste materials. More specifically, the present invention is directed to such gate valve systems as are equipped with an external self-closing mechanism that can be remote and temperature actuated as well as manually operated.
2. Description of Related Art
Tank trucks used for the transportation of liquid and semi-solid materials typically have at least one loading/unloading outlet in the form of pipe-type member to which a hose may be detachably connected for directing the load being discharged into a receiving tank or the like. To start and stop the flow through the unloading outlet, the outlet is usually equipped with a gate valve. Such gate valves are well known and are manually actuated by an actuating lever being swung in an arc, thereby raising and lowering a closure disc within the valve body between a closed position seated against a valve seat and blocking the outlet opening, and and an open position shifted radially relative to the closed position. One commercial source for tank truck gate valves is CFI Valve Specialties of Berkeley, Calif.
Existing and proposed government regulations, for example, the U.S. Department of Transportation (DOT) rules for cargo tanks (see, .sctn.178.345-11 of Docket 183) dictate that tank outlets be fitted with an external self-closing system which is capable of closing the outlet within 30 seconds and which is remotely actuatable at a distance of at least 10 feet. Furthermore, such DOT regulations require that tanks being used to transport flammable, pyrophoric, oxidizing or Poison B liquids, such as fuels and hazardous waste materials, have a self-closing system that is, additionally, capable of being thermally activated to close at temperatures not to exceed 250.degree. F. as a safeguard in the case of a fire.
Tank outlet gate valves with actuators that can meet the above-mentioned DOT regulations are available; for example, from the noted CFI Valve Specialties. However, such self-closing actuators are hydraulically operated and are not suitable for retrofit installation on gate valves that are currently only manually actuatable. Thus, such actuators are high in cost, and require replacing of the existing valve on tanks currently in service, in most instances.
Thus, there is a need for a self-closing actuator for gate valves which will meet all of the regulations pertaining to hazardous cargoes, yet will be low in cost and can be retrofit installed on existing tank gate valves in a simple and easy manner.